Packaging materials used for food products or pharmaceutical products are required to protect the product inside from being degraded. For example, packaging materials for food products are required to reduce oxidation or degradation of protein, oil and fat or the like and thereby to preserve flavor and freshness. Further, packaging materials for pharmaceutical products that should be handled under aseptic conditions are required to protect the active ingredients of the product from being degraded in order to preserve the efficacy of the ingredients.
Such degradation of the products is mainly caused by oxygen or moisture that penetrates through the packaging material or other gases that are reactive to the product. Accordingly, packaging materials used for food products or pharmaceutical products are required to have properties that do not allow gases such as oxygen and moisture to penetrate therethrough (gas barrier properties).
In order to meet such requirements, gas barrier films formed of a polymer having relatively high gas barrier properties (gas barrier polymer) or a laminate (laminate film) which uses the gas barrier film as a substrate film have been used.
Conventionally, polymers containing a highly hydrophilic hydrogen bonding group in a molecule, which is represented by poly(meth)acrylic acid or polyvinyl alcohol, have been used as gas barrier polymers. Packaging materials made of such polymers exhibits good gas barrier properties to oxygen or the like under dry conditions. However, packaging materials made of such polymers have a problem in that gas barrier properties to oxygen or the like are significantly impaired due to hydrophilicity under a condition of high humidity and that resistance to humidity or hot water is poor.
In order to solve these problems, it is known to obtain a gas barrier packaging material by laminating a polycarboxylic acid polymer layer and a polyvalent metal compound-containing layer in an adjacent manner on a substrate so that polycarboxylic acid polymer reacts with a polyvalent metal compound between two layers of the polycarboxylic acid polymer layer and the polyvalent metal compound-containing layer to generate a polyvalent metal salt of the polycarboxylic acid polymer (for example, see PTLs 1 and 2). The gas barrier packaging material thus obtained is known to have high oxygen gas barrier properties under a condition of high humidity.